Due to the rising cost of liquid fuel (e.g. diesel fuel) and ever increasing restrictions on exhaust emissions, engine manufacturers have developed dual-fuel engines. An exemplary dual-fuel engine provides injections of a low-cost gaseous fuel (e.g. natural gas) through air intake ports of the engine's cylinders. The gaseous fuel is introduced with clean air that enters through the intake ports and is ignited by liquid fuel that is injected during each combustion cycle. Because a lower-cost fuel is used together with liquid fuel, cost efficiency may be improved. In addition, the combustion of the gaseous and liquid fuel mixture may result in a reduction of harmful emissions.
An exemplary dual fuel engine is disclosed in U.S. Pat. No. 5,035,206 that issued to Welch et al. on Jul. 30, 1991. In particular, the '206 patent discloses a dual-fuel engine having an engine cylinder with a gaseous fuel injector for injecting natural gas into the combustion chamber to mix with separately-injected diesel fuel. The gaseous fuel injector includes a delivery conduit mounted at a location above cylinder intake ports. This location above the intake ports may allow for injection of the gaseous fuel later in the cycle, such as after the intake ports have been closed by the piston.
While the dual-fuel engine of the '206 patent may result in lower operating costs and/or exhaust emissions, it may be less than ideal. In particular, it may be possible for fuel that is injected while the intake ports are open to escape through another one of the ports. Further, injecting fuel after the intake ports are closed may result in inefficient mixing of the fuel and intake air. Also, in order to install the delivery conduit above the intake ports, modification of the cylinder may be necessary to include an aperture that accommodates the conduit. This extra fabrication step may reduce retrofit applicability.
The disclosed fuel system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.